Preparation of chromium complexes of beta-diketones



United States Patent 3,134,797 PREPARATION OF CHROMIUM COMPLEXES OF ,B-DIKETONES Kirman Taylor, Painesville, Ohio, assignor to Diamond Alkali Company, Cleveland, Ohio, a corporation of Delaware No Drawing. Filed June 13, 1960, Ser. No. 35,437 12 Claims. (Cl. 260-438) This invention relates to a method for the preparation of chromium organic compounds and more particularly relates to a method of preparing compounds, such as chromium acetylacetonate, by the reaction of an anhydrous chromic chloride source material and an organic compound selected from the group consisting of organic compounds which undergo keto-enol tautomerism and organic compounds which have a hydroxy group positioned with regard to a coordinating atom so as to be capable of forming, with the chromium of the chromic chloride source material, a ring having -7 members.

In recent years, compounds of this type, and particularly chromium acetylacetonate, have been the subject of a great deal of interest. This interest has been generated by the fact that these compounds are useful as additives in rubber, petroleum products, plastics, asphalts, paints, and the like, as catalysts and intermediates in organic syntheses and manufacturing processes and additionally as a source of chromium metal in plating or coating operations. In this latter application, inasmuch as these compounds are soluble in many organic solvents, they are particularly useful in processes involving chromium plating from organic solutions as well as being usable in vapor plating or coating processes.

However, the widespread use of these compounds has been somewhat stymied in that up to the present time no completely satisfactory method has been found by which they may be economically produced. In this regard, although many processes have been proposed for preparing these compounds, and in particular chromium acetylacetonate, they all have one thing in common and that is that the preparation involves the use of an aqueous systern.

In the eariler of these processes, the product yield, i.e., chromium acetylacetonate, was very low, due principally to the coprecipitation of chromic hydroxide during the reaction. In later processes, efforts have been made to overcome this difficulty, such as for example, by using freshly precipitated hydrous chromium oxide as the source of chromium. However, this procedure necessitates an excess of the organic reagent, i.e., acetylacetone, which is the most expensive of the initial reactants, and is subject to further difiiculties in that the hydrous chromium oxide must be prevented from aging if it is to be used. In a more recent process, described in U.S.Patent 2,823,- 217, an attempt is made to overcome the difficulties of the prior are processes by the addition of an alkali 'carboxy methyl dextran to the reaction mixture in order to prevent the precipitation of the chromium hydroxide. Although this latter process has seemingly been successful in that the precipitation of the chromium hydroxide is substantially prevented, it will be appreciated that this advantage is obtained only by the disadvantage of adding a somewhat costly chemical to the reaction mixture. Additionally, in this process although only stoichiometric quantities of the reactants are used, the yield of the chromium acetylacetonate is only about 83% and difliculties are encountered in extracting the remaining portions of the organic reagent acetylacetone, from the water in order that it may be reused. Thus, it will be apparent that none of the prior processes have been completely 3,134,797 Patented May 26, 1964 successful in overcoming the problems encountered in the production of these chromium organic compounds, and particularly chromium acetylacetonate, primarily, because these processes have attempted to minimize the effect of the precipitation of chromium hydroxide rather than eliminating its cause.

It is, therefore, an object of the present invention to provide a novel method of preparing chromium acetylacetonate and similar chromium organic compounds wherein no chromium hydroxide is produced to interfere with the production of the organic chromium compound.

A further object of the present invention is to provide a method for producing chromium acetylacetonate and similar organic compounds wherein substantially stoichiometric amounts of the reactants can be used and suband organic compounds which have a hydroxy group positioned with regard to a coordinating atom so as to be capable of forming, with the chromium of the chromic 1 chloride source material, a ring having 5-7 members. The

reaction is carried out in a non-aqueous solution by boiling or refluxing the reaction mixture, after effecting solubilization of the chromic chloride source material. By utilizing a non-aqueous solution for carrying out this reaction, there is no precipitation of chromium hydroxide and the problems previously encountered because of such precipitationare eliminated.

Exemplary of the organic compounds which undergo keto-enol tautomerism and may be used in the present method are the beta-diketones, such as acetyland benzoyl-acetone, and the beta-dioximes. Of the organic compounds capable of forming, with chromium, 5-7 membered rings, those compounds having a hydroxy group in a position alpha or beta to a coordinating group, such as an oxygen or nitrogen atom, are typical. Exemplary of such compounds are salicylic acid and its derivatives, Z-hydroxyazo compounds, S-hydroxyquinoline, l-hydroxyanthraquinone and alpha-hydroxy acids. Of these, excellent results have been obtained when using acetylacetone as the organic compound and for this reason, hereinafter, primary reference will be made thereto and to the preparation of chromium acetylacetonate. It is to be understood, however, that the method of the present invention is applicable when using any of the organic compounds which will undergo a keto-enol tautomerism so that the specific references to acetylacetone and chromium acetylacetonate are intended to be merely illustrative .of the invention and not limiting.

The source of chromium for use in the present method may come from anhydrous chromic chloride or from organic complexes of anhydrous chromic chloride. Of the latter, the preferred is a complex of anhydrous chromic chloride and acetone. The preparation of this organic complex of anhydrous chromic chloride, as Well as that 0, 12 The method of the present invention may be illustrated generally by the following empricical formula:

Reflux 4 Hours CIC13+ BCH COHCHCOCI-h Cr(CH C CEO 0 01193 3HC1 In carrying out this reaction, it has been found that in order to assure that the reaction will proceed at a satisfactory rate, it is necessary to solubilize the chromic chloride by adding a catalyst, such as metallic zinc or chromous chloride to the reaction mixture. Excellent results have been obtained using chromous chloride as the catalyst and for this reason it is preferred in the present method. It has further been found, that if a freshly distilled acetylacetone is used in carrying out the reaction, the reaction will proceed at a satisfactory rate without the necessity of using a catalyst. However, as those skilled in the art will undoubtedly appreciate, some difiiculties may be encountered in adapting the present process to commercial production, particularly, as a continuous process, where freshly distilled acetylacetone is required and for this reason it is preferred to carry out the reaction using a catalyst. It has also been found that when using a catalyst, the best results are obtained when the reaction mixture contains no moisture. It is believed that when there is moisture present in the system, the moisture acts to poison the chromous chloride catalyst, thereby rendering it non-effective in catalyzing the reaction.

Where the source of chromic chloride used in the present method is one of the organic complexes of chromic chloride, such as the acetone complex, it has been found that the reaction with acetylacetone progresses at a satisfactory rate without the necessity for the addition of a catalyst, such as chromous chloride or zinc. Inasmuch as it is believed that the catalyst serves primarily to solubilize the chromic chloride, since the organic complexes of chromic chloride are considerably more soluble than chromic chloride itself, no catalyst is needed. Additionally, in this reaction, the reaction mixture is boiled for a sufiicient amount of time to distill off the acetone or other organic solvent.

Inasmuch as in the present reaction, the most expensive of the raw materials is the acetylacetone, it has been found to be desirable to carry out the reaction in benzene or a similar organic solvent, as the reaction medium. This is particularly true when the process is to be carried out continuously. In such an operation, substantially stoichiometric quantities of the acetylacetone are dissolved in benzene and following the reaction, the benzene containing any unreacted acetylacetone is recycled. In this manner, the need for recycling a large quantity of the relatively expensive acetylacetone is eliminated by ecycling the relatively inexpensive organic solvent, such as benzene, in which is dissolved the small quantities of unreacted acetylacetone.

In carrying out the method of the present invention, the reaction mixture, consisting of the chromic chloride source material, e.g., anhydrous chromic chloride, and acetylacetone, in substantially stoichiometric amounts, are refluxed for a period of about 2 to 6 hours, preferably about 4 hours, in benzene in the presence of a catalyst, e.g., chromous chloride. The amount of catalyst used is not in excess of about 1% by Weight of the total reaction mixture, excluding the benzene, and generally is only about 0.2% by weight of the total reaction mixture. The chromium acetylacetonate thus formed is recovered by recrystallization from benzene and washed with an aqueous solution of ammonium hydroxide. The chromium acetylacetonate thus recovered is found to be quite stable, undergoing decomposition only to the extent of about 1.2% by weight after heating for hours at 191 C. and additionally is substantially water-insoluble,

, being soluble only to the extent of about 0.15%.

I11 order that those skilled in the art may better understand the method of the present invention and the manner in which it may be practiced, the following specific examples are given.

Example 1 Analysis Theoretical Actual Percent Cr 14. 14. 70 Percent 01.. 0.00 0. 02 Percent C... 51.60 52.00 Percent H 6. 06 6. 00 Melting Point, 216 216 Example 2 Twenty (20) grams CrCl and grams redistilled acetylacetone (B.P. 7 C.) are refluxed in a 300 ml. round bottom flask for about 4 hours. The mixture is cooled to room temperature and the chromium acetylacetonate filtered oil. The resulting product is then recovered as in Example 1. The yield of chromium acetylacetonate, based on the CrCl used, is substantially quantitative.

Example 3 Twenty (20) grams CrCl 400 ml. dry benzene, 45 ml. of acetylacetone and 0.1 gram CrCl are refluxed in a 1-liter Wide mouth Erlenmeyer flask for about 5 hours. All solvent is removed by evaporation and chromium acetylacetonate crystals are washed with ether and an aqueous ammonical solution. Essentially a quantitative yield of chromium aeetylacetonate, based on the CrCl used is obtained.

Example 4 Ten (10) grams of trichlorotriacetonechromium (III), prepared in accordance with the procedure of US. Ser. No. 828,009, are dissolved in 40 ml. of acetylacetone. The solution is heated to boiling and the acetone is distilled out. During the distillation the dark green liquor changed to a red-violet color and chromium acetylacetonate crystals are precipitated. The mixture is cooled to room temperature and the chromium acetylacetone product recovered as in Example 1. The yield of chromium aeetylacetonate, based on the trichlorotriacetonechromium (III) used, is substantially quantitative.

While there have been described various embodiments of the invention, the methods described are not intended to be understood as limiting the scope of the invention, as it is realized that changes therewithin are possible, and it is further intended that each element recited in any of the following claims is to he understood as referring to all equivalent elements for accomplishing substantially the same results in substantially the same or equivalent manner, it being intended to cover the invention broadly in whatever form its principle may be utilized.

What is claimed is:

1. A method of preparing a chromium organic compound which comprises combining, under anhydrous conditions, a chromic chloride source material selected from the group consisting of anhydrous chromic chloride and organic complexes of anhydrous chromic chloride having the formula ClClg'XR, wherein R is selected from the group consisting of ketones, aldehydcs, alcohols, acid esters, amides and amines and X is a number from 1 to 4, inclusive, with an organic compound selected from the group consisting of acetylacetone and benzoyl acetone in an organic solvent selected from the group consisting of said organic compound and benzene, adding a catalyst selected from the group consisting of metallic zinc and chromous chloride, refluxing the thus formed reaction mixture for a period of time sufficient to effect a reaction between the chromic chloride source material and the organic compound to form a chromium organic compound and recovering the said organic chromium compound.

2. The method as claimed in claim 1 wherein the reaction medium is benzene.

3. A method of preparing chromium acetylacetonate which comprises combining, under anhydrous conditions, a chromic chloride source material selected from the group consisting of anhydrous chromic chloride and organic complexes of anhydrous chromic chloride having the formula Crcl -XR, wherein R is selected from the group consisting of ketones, aldehydes, alcohols, acid esters, amides and amines and X is a number from 1 to 4, inclusive, with acetylacetone in an organic solvent selected from the group consisting of acetylacetone and benzene, adding a catalyst selected from the group consisting of metallic zinc and chromous chloride, refluxing the thus formed reaction mixture for a period of time sufficient to eflect a reaction between the chromic chloride source material and the acetylacetone to produce chromium acetylacetonate and recovering the chromium acetylacetonate.

4. The method as claimed in claim 3 wherein the reaction medium is benzene.

5. A method of preparing chromium acetylacetonate which comprises combining anhydrous chromic chloride and acetylacetone in an organic solvent selected from the group consisting of acetylacetone and benzene, adding a catalyst selected from the group consisting of metallic zinc and chromous chloride, refluxing the thus formed reaction mixture for a period of time suflicient to efiect a reaction between the anhydrous chromic chloride and the acetylacetone to form chromium acetylacetonate and recovering the chromium acetylacetonate.

6. The method as claimed in claim 5 wherein the catalyst is chromous chloride.

7. The method as claimed in claim 6 wherein the reaction medium is benzene.

8. The method as claimed in claim 5 wherein the reaction medium is benzene.

9. A method of preparing chromium acetylacetonate which comprises combining trichlorotriacetonechromium (III) and acetylacetone in an organic solvent selected from the group consisting of acetylacetone and benzene, heating the thus formed reaction mixture for a period of time suflicient to effect a reaction between the trichlorotriacetonechromium (III) and the acetylacetone and distill off acetone to form chromium acetylacetonate and recovering the chromium acetylacetonate.

10. A method of preparing chromium acetylacetonate which comprises combining trichlorotriacetonechromium (III) and acetylacetone in benzene, heating the thus formed reaction mixture for a period of time sufficient to efiect a reaction between the trichlorotriacetonechromium (III) and the acetylacetone and distill ofif acetone to form chromium acetylacetonate and recovering the chromium acetylacetonate.

11. A method of preparing chromium acetylacetonate which comprises combining trichlorotriacetonechromium (III) and acetylacetone, heating the thus formed reaction mixture for a period of time sufficient to effect a reaction between the trichlorotriacetonechromium (III) and the acetylacetone and distill 01f acetone to form chromium acetylacetonate and recovering the chromium acetylacetonate.

12. A method of preparing chromium acetylacetonate which comprises combining anhydrous chromic chloride and freshly distilled acetylacetone under anhydrous conditions, refluxing the thus formed reaction mixture for a period of time suificient to eiIect a reaction between the chromic chloride and the acetylacetone to form chromium acetylacetonate and recovering the chromium acetylacetonate and recovering the chromium acetylacetonate.

References Cited in the file of this patent Chemical Elements and Their Compounds, Sidgwick, vol. 11, page 1012, 1950.

Inorganic Syntheses, vol. V, 1957, page -116.

Patent No. 3,134, 797 May 26 1964 Kirman Taylor It is hereby certified that error a ent requiring correction and that the sa corrected below.

ppears in the above numbered patid Letters Patent should read as Column 1, line 57, for "are" read art line 67, for "3,9076, 833" read 3 ,076 ,833 column 6, lines 35 and 36, after "chromium acetylacetonate" strike out "and recovering the chromium acetylacetonate".

; column 2,

Signed and sealed this 13th day of October 1964.

(SEAL) Attest:

ERNEST W; SWIDER Attesting Officer EDWARD J. BRENNER Commissioner of Patents 

1. A METHOD OF PREPARING A CHROMIUM ORGANIC COMPOUND WHICH COMPRISES COMBINING, UNDER ANHYDROUS CONDITIONS, A CHROMIC CHLORIDE SOURCE MATERIAL SELECTED FROM THE GROUP CONSISTING OF ANHYDROUS CHROMIC CHLORIDE AND ORGANIC COMPLEXES OF ANHYDROUS CHROMIC CHLORIDE HAVING THE FORMULA CRCL3 XR, WHEREIN R IS SELECTED FROM THE GROUP CONSISTING OF KETONES, ALDEHYDES, ALCOHOLS, ACID ESTERS, AMIDES AND AMINES AND X IS A NUMBER FROM 1 TO 4, INCLUSIVE, WITH AN ORGANIC COMPOUND SELECTED FROM THE GROUP CONSISTING OF ACETYLACETONE AND BENZOYL ACETONE IN AN ORGANIC SOLVENT SELECTED FROM THE GROUP CONSISTING OF SAID ORGANIC COMPOUND AND BENZENE, ADDING A CATALYST SELECTED FROM THE GROUP CONSISTING OF METALLIC ZINC AND CHROMOUS CHLORIDE, REFLUXING THE THUS FORMED REACTION MIXTURE FOR A PERIOD OF TIME SUFFICIENT TO EFFECT A REACTION BETWEEN THE CHROMIC CHLORIDE SOURCE MATERIAL AND THE ORGANIC COMPOUND TO FORM A CHROMIUM ORGANIC COMPOUND AND RECOVERING THE SAID ORGANIC CHROMIUM COMPOUND. 